The present invention relates to a method for controlling the inverter by means of space vector modulation, in particular for controlling an electrical machine, wherein the inverter has a plurality of controllable switches and is designed to provide a polyphase electric current, in particular in order to supply the electrical machine with electric current in a polyphase fashion, wherein a nominal current space vector having a nominal phase angle and a nominal amplitude is predefined, wherein the inverter is controlled such that a plurality of different consecutive switching states of the switches are set in order to provide the electric current in the form of a current space vector.
The present invention also relates to a device for controlling an inverter, in particular for controlling an electrical machine, wherein the inverter has a plurality of controllable switches which are connected to provide a polyphase electric current as a function of a nominal current space vector having a nominal phase angle and a nominal amplitude, in particular to energize the electrical machine in a polyphase fashion, having a control device which is designed to control the inverter such that the switches of the inverter assume a plurality of consecutive different switching states in order to provide the electric current in the form of a current space vector.
Finally, the present invention relates to a motor vehicle drivetrain having at least one electrical machine for providing drive power, an inverter for controlling the electrical machine and having a device for controlling the inverter of type described above.
Various control methods are known in the technical field of three-phase loads in general and of three-phase electrical machines in particular. In this case, the method of space vector modulation is currently usually preferable for controlling the three-phase load. In the case of this control method, a space vector is formed by consecutive setting of eight basic voltage phasors. In order to provide the string voltage, the basic voltage phasors are switched in a pulse-width-modulated manner, with the result that a corresponding control voltage is generated.
In the case of the known control methods, the electrical loads are controlled by means of an inverter with power semiconductor switches. The eight consecutive basic voltage phasors for generating the voltage space vector are set by virtue of particular power semiconductor switches of the inverter being alternately switched on and off. In the case of very low rotation speeds of the space vector or, provided the three-phase load is an electrical machine, in the case of low speeds of the controlled electrical machines, individual ones of the power semiconductor switches are switched very often or for a very long time and are thus thermally loaded with an electric current which flows for a very long time or very often. Therefore, the power semiconductor switches must be configured for very long switch-on times and for very large currents, which results in the inverter being generally elaborate in terms of technology.
In order to respond to an overload, in particular a thermal overload, of the power semiconductor switches, it is proposed in WO 2010/000548 A2, for example, to omit one of two switching states which switch so as to be free of voltage in particular pulse-width-modulation periods in order to reduce the switching losses of the power semiconductor switches.
Since the loading, in particular thermal loading, of individual power semiconductor switches of the inverter is dependent on a phase angle of the provided current space vector or individual ones of the power semiconductor switches of the inverter are differently loaded for particular phase angles of the provided current space vector, it is proposed in DE 10393516 T1, for example, to use a particular zero vector in particular angular regions of the provided current space vector in order to reduce the switching losses of the power semiconductor switches.
It is disadvantageous here that, in different control situations and in the case of different rotation speeds of the current space vector, individual ones of the power semiconductor switches are loaded more heavily and, therefore the inverter is loaded unevenly in particular situations and in other situations in which the power semiconductor switches are loaded substantially evenly, the efficiency of the current use is reduced.